train went off the rails and then hit another. It happened at the height of rush hour on one of the nation's busiest routes from grand central station to boston. Marcie gonzalez tonight on the critical injuries and the relief that the outcome wasn't far worse. Reporter:24 hours after two commuter trains packed with passengers collided in connecticut, the twisted wreckage remains. Our cameras the only one there as ntsb investigators took a first look saying it could be weeks before they know why this happened. The cause of the accident while we're on the scene, nor will we speculate on what may have caused the accident. Reporter: This crash would have been much worse. It was the height of the friday evening rush when a metro north train left new york city passing near bridgeport, connecticut when it somehow derailed. It sent cars directly into the path of an on coming train on the adjacent tracks. One of those jolts that sent people flying. Reporter: Of the 700 people on board those trains, 70 were hurt. Senator blumenthal says that number would likely be higher if not for the new rail cars put in operation two years ago. Perhaps injuries were avoided because these were better cars. Reporter: David we're told it could be days before these trains are finally moved which would mean headaches for thousands of commuters in the northeast as they try to make their way to work on monday morning.

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